Mark Zuckerberg might - just maybe - want to start considering how far in advance big entertainment acts need to be booked. Because, according to new comScore stats, it looks like his social network could be celebrating an important victory over MySpace in about twelve months.

FaceBook have 54.5 million monthly unique visitors, says Comscore, compared to nearly 76 million for MySpace. ButFacebook’s growth rate in the U.S. averaged 3.8% per month over the last twelve months. MySpace’s U.S. growth rate is 0.8% per month. That’s nothing to be ashamed of, but unless things change a lot, Facebook will overtake MySpace to become the largest social network in the U.S. in…2010.

At current growth rates Facebook will overtake MySpace in January 2010, a year from now. That is the month Facebook will reach 86 million U.S. users, compared to MySpace’s 84 million in January. Will this prediction be correct? Probably not, but it’s the best guess given today’s data.

It may actually take longer. Facebook’s growth rate had been increasing as the year wore on but dipped in December. As they get closer to MySpace it may become ever harder to catch up.